Polarizing plate

ABSTRACT

A polarizing plate has a polarizer and a protective film formed on at least one surface of the polarizer. The protective film is formed by curing an energy ray-curable composition that contains at least one of a first energy ray-polymerizing compound having a bisphenol residue, a second energy ray-polymerizing compound having a neopentylglycol group, a third energy ray-polymerizing compound having a trimethylolpropane group, and a fourth energy ray-polymerizing compound having a pentaerythritol group. In the polarizing plate, though the protective film is thin, the polarizer is protected from the influence of external moisture, etc., and therefore its polarizability is kept good even in high-temperature high-humidity environments.

This application is a 371 of PCT/JP02/13431 filed Dec. 24, 2002.

TECHNICAL FIELD

The present invention relates to a polarizing plate.

BACKGROUND ART

Heretofore, polarizing plates are used in optical devices such asliquid-crystal display devices, organic EL display devices, glasses andothers, and the polarizing plates for such applications are generallyconstructed by sticking, with an adhesive, protective films on bothsurfaces of a polarizer formed of an iodine-colored, uniaxial-orientedpolyvinyl alcohol resin film, for improving the strength, the waterresistance and the moisture resistance of the polarizer.

For the protective film for such polarizing plates, used is an acetylcellulose resin film (TAC film) of good optical transparency; and ahydrophilic adhesive is used for them, taking the matter intoconsideration that both the polarizer and the protective film arehydrophilic.

In the above-mentioned polarizer, the coloring polyiodide ions (e.g., I₃⁻, I₅ ⁻) exhibits the polarizability thereof as a result of the uniaxialorientation of the polyvinyl alcohol resin film. Therefore, when thepolarizer receives moisture (water vapor), then the polyiodide thereindecomposes into iodide ions (I⁻) and the coloration by the polyiodideions is thereby reduced. This phenomenon is more remarkable inhigh-temperature environments. As a result, it is considered that thetransmittance of the polarizer may increase and the polarizer may loseits polarizability. Accordingly, protective films for polarizing platesare required to have the ability to protect polarizers from theinfluence of external moisture and others thereon.

However, taking the matter into consideration that both the TAC film andthe adhesive in conventional polarizing plates are hydrophilic, thethickness of the TAC film has heretofore made to be at least about 80 μmin order that the film may protect polarizers from the influence ofexternal moisture thereon. Accordingly, conventional polarizing platesare problematic in that they could not satisfy the requirement in therecent art of optical display devices that the protective films forpolarizing plates for such devices are thinned as much as possible (forexample, their thickness is reduced to at most 40 μm).

DISCLOSURE OF THE INVENTION

The present invention is to solve the above-mentioned problems with therelated art, and its object is to make it possible to protect polarizersfrom the influence of external moisture and others thereon even when theprotective films for them in polarizing plates are thinned.

The present inventors have found that, when a protective film formed ofa curable composition that contains an energy ray-polymerizing compoundhaving a specific substituent is provided on at least one surface of apolarizer, then it can attain the above-mentioned object, and havecompleted the present invention.

Specifically, the present invention provides a polarizing plate having apolarizer and a protective film formed on at least one surface of thepolarizer, wherein the protective film is formed by curing an energyray-curable composition that contains at least one of a first energyray-polymerizing compound having a bisphenol residue, a second energyray-polymerizing compound having a neopentylglycol group, a third energyray-polymerizing compound having a trimethylolpropane group, and afourth energy ray-polymerizing compound having a pentaerythritol group.

The present invention also provides a liquid-crystal display devicehaving a liquid-crystal panel and the above-mentioned polarizing plateprovided on at least one surface of the liquid-crystal panel.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic cross-sectional view of a liquid-crystal displaydevice with polarizing plates of the prensent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail hereinunder.

The polarizing plate of the present invention is constructed by forminga protective film on at least one surface of a polarizer. The protectivefilm is formed by irradiating an energy ray-curable composition thatcontains at least one of first to fourth energy ray-polymerizingcompounds, especially an energy ray-curable composition that containsboth a first energy ray-polymerizing compound and a second energy ray,with energy rays such as UV rays or electron rays to thereby polymerizeand cure the energy ray-polymerizing compounds in the composition.

Accordingly, even when the thickness of the protective film in thepolarizing plate of the present invention is reduced to at most about 40μm, the film is still effective for protecting the polarizer thereinfrom the influences of external moisture and others. In addition, theprotective film may function also as a support for the polarizer.

Preferably, the energy ray-curable composition to form the protectivefilm is so designed that, when it contains a first energyray-polymerizing compound, then the content of the compound is at least20% by weight in terms of the resin solid content thereof; when itcontains a second energy ray-polymerizing compound, then the content ofthe compound is at least 40% by weight in terms of the resin solidcontent thereof; and when it contains a third energy ray-polymerizingcompound, then the content of the compound is at least 60% by weight interms of the resin-solid content thereof. If the content of these energyray-polymerizing compounds is too low, then it will be difficult tomaintain the polarizability of the polarizer.

The bisphenol group in the first energy ray-polymerizing compound isrepresented by the following general formula (1):

where in formula (1), R represents a hydrogen atom or a methyl group.

The bisphenol group includes, for example, a bisphenol A-type group ofthe following general formula (2), and a bisphenol F-type group of thefollowing general formula (3):

The neopentylglycol group in the second energy ray-polymerizing compoundis represented by the following general formula (4):

The trimethylolpropane group in the third energy ray-polymerizingcompound is represented by the following general formula (5):

The pentaerythritol group in the fourth energy ray-polymerizing compoundis represented by the following general formula (6):

The main part that contributes to the polymerization of the first tofourth energy ray-polymerizing compounds is, for example, a(meth)acryloyl residue that contains an acryloyl or methacryloyl groupas a part thereof. The (meth)acryloyl residue (CH₂═CRCO—, in which Rrepresents a hydrogen atom or a methyl group) may bond to theneopentylglycol, pentaerythritol, trimethylolpropane or bisphenol group,via an oxygen atom (—O—) (that is, as a (meth)acryloyloxy group), or viaan oxyalkyleneoxy group (—O(CH₂)_(n)O—, —O(CH₂)_(m)O—, in which n and meach indicate an integer of from 1 to 10) therebetween.

The residue may also bond to the group via an EO (ethyleneoxide)-modified residue, a PO (propylene oxide)-modified residue, anepoxy-modified residue or a modified residue of their combination. Forexample, the (meth)acryloyl residue may bond to the bisphenol group via—O(CH₂CH₂O)_(n)—, —O(CH(CH₃)CH₂O)_(n)—, —O(CH₂CH₂O)_(m)—, or—O(CH(CH₃)CH₂O)_(m)—. In these, n and m each indicate an integer of from1 to 10.

Preferred examples of the first energy ray-polymerizing compound arecompounds of the following chemical formulae (a) and (b). Chemicalformula (a) indicates a first energy ray-polymerizing compound having abisphenol A group; and chemical formula (b) indicates a first energyray-polymerizing compound having a bisphenol F group.

In formulae (a) and (b), R represents a hydrogen atom or a methyl group;X represents —O—, —O(CH₂CH₂O)_(n)— or —O(CH(CH₃)CH₂O)_(n)—; Y represents—O—, —O(CH₂CH₂O)_(m)— or —O(CH(CH₃)CH₂O)_(m)—; n and m each indicate aninteger of from 1 to 10.

Specific examples of the first energy ray-polymerizing compound areEO-modified bisphenol A diacrylate (SR-349 by Sartomer; R-551 by NipponKayaku), EO-modified bisphenol F diacrylate (R-712 by Nippon Kayaku),epoxy-modified bisphenol A dimethacrylate (Epoxy Ester 3002M by KyoeiChemical), epoxy-modified bisphenol A acrylate (Epoxy Ester 3002A byKyoei Chemical), diglycidyl ether-modified bisphenol A dimethacrylate(Epoxy Ester 3000M by Kyoei Chemical), diglycidyl ether-modifiedbisphenol A diacrylate (Epoxy Ester 3000A by Kyoei Chemical).

Preferred examples of the second energy ray-polymerizing compound arecompounds of the following chemical formulae (c) to (e).

Preferred examples of the third energy ray-polymerizing compound arecompounds of the following chemical formulae (f) and (g).

Preferred examples of the fourth energy ray-polymerizing compound arecompounds of the following chemical formulae (h) and (i).

The energy ray-curable composition to form the protective film in thepresent invention may contain, if desired, at least one or more energyray-polymerizing compounds selected from the first, third and fourthenergy ray-polymerizing compounds and optionally a fifth energyray-polymerizing compound mentioned below, in addition to the secondenergy ray-polymerizing compound in the composition.

Specific examples of the fifth energy ray-polymerizing compound includeethylenic unsaturated monomers. Concretely, they includemethyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-butyl(meth)acrylate, t-butyl(meth)acrylate, 2-ethylhexyl (meth)acrylate,n-nonyl(meth)acrylate, cyclohexyl (meth)acrylate, benzyl(meth)acrylate,dicyclopentenyl (meth)acrylate, 2-dicyclopentenoxy(meth)acrylate,methoxyethyl(meth)acrylate, ethoxyethyl(meth)acrylate,butoxyethyl(meth)acrylate, methoxyethoxyethyl (meth)acrylate,ethoxyethoxyethyl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate,carbitol acrylate, benzyl acrylate, allyl acrylate, phenoxyethylacrylate, styrene, vinyltoluene, chlorostyrene, α-methylstyrene,acrylonitrile, vinyl acetate, N-vinylpyrrolidone, acryloxyethylphosphate, 2-vinylpyridine, 2-ethylhexyl acrylate,2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl acrylate, ethylcarbitolacrylate, polypropylene glycol diacrylate, polyethylene glycol (#200,#400, #600) diacrylate, 2-hydroxy-3-phenoxypropyl acrylate,2-acryloyloxyethylsuccinic acid, 1,6-hexanediol diacrylate,trimethylolpropane triacrylate, EO (ethylene oxide)-modifiedtrimethylolpropane triacrylate, methyltriglycol, acryloylmorpholine,1,9-nonanediol diacrylate, 2-n-butyl-2-ethyl-1,3-propanediol diacrylate.Their oligomers are also usable herein. In addition, polyester(meth)acrylates, urethane (meth)acrylates, polybutadiene(meth)acrylates, isoprene acrylates and epoxyacrylates are also usableherein. In particular, polyester (meth)acrylates such as acrylates ofaliphatic polyesters (e.g., polyester of adipic acid with ethyleneglycol) are preferably used in the composition.

When the fifth energy ray-polymerizing compound is used in the energyray-curable composition, its amount may be at most 95% by weight,preferably at most 80% by weight of the composition, though depending onthe type of the compound. If the amount of the compound oversteps therange, the content of the other energy ray-polymerizing compounds may bereduced relatively to it and, if so, the effect of the present inventioncould not be attained.

In the polarizing plate of the present invention, also usable is theenergy ray-curable composition that contains the third energyray-polymerizing compound, and at least one of the first, second, fourthand fifth energy ray-polymerizing compounds added thereto.

Also usable is the energy ray-curable composition that contains thefourth energy ray-polymerizing compound, and at least one of the firstto third and fifth energy ray-polymerizing compounds added thereto.

Still usable is the energy ray-curable composition that contains amixture of the first and second energy ray-polymerizing compounds, andat least one of the third to fifth energy ray-polymerizing compoundsadded thereto.

In order that the energy ray-curable composition polymerizes and cures,it is desirable that any of the energy ray-polymerizing compounds in thecomposition is a polyfunctional compound, for example, containing 2 ormore (meth)acryloyl residues in one molecule. If desired, thecomposition may contain a known crosslinking agent such as apolyisocyanate-type crosslinking agent.

The energy ray-curable composition may contain an energy raypolymerization initiator. The energy ray polymerization initiator may besuitably selected, for example, from cobalt octenoate, cobaltnaphthenate, manganese octenoate, manganese naphthenate, methyl ethylketone peroxide, cyclohexanone peroxide, cumene hydroperoxide, benzoylperoxide, dicumyl peroxide, t-butyl perbenzoate, benzoin, benzoin methylether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butylether, benzoin phenyl ether, anthraquinone, naphthoquinone, pivaloinethyl ether, benzyl ketal, 1,1-dichloroacetophenone,p-t-butyldichloroacetophenone-, 2-chlorothioxanthone,2,2-diethoxyacetophenone, Michler's ketone,2,2-dichloro-4-phenoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone,benzophenone, 2-methylthioxanthone, phenyl glyoxylate,α-hydroxyisobutylphenone, dibenzosuberone, benzophenone-amines (e.g.,N-methyldiethanol, triethylamine), benzyldiphenyl disulfide,tetramethylthiuram monosulfite, azobisisobutyronitrile, dibenzyl,diacetyl, acetophenone, 2,2-dimethoxy-2-phenylacetophenone,2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone,1-hydroxycyclohexyl phenyl ketone,2-hydroxy-2-methyl-1-phenylpropan-1-one-methyl benzoylformate, dependingon the type of the energy ray used for the composition.

The amount of the energy ray polymerization initiator to be in thecomposition is not specifically defined, but is preferably from 0.1 to15 parts by weight, more preferably from 0.5 to 10 parts by weightrelative to 100 parts by weight, in terms of the resin solid contentthereof, of the total weight of the energy ray-polymerizing compounds inthe composition.

If desired, the energy ray-curable composition in the present inventionmay contain an organic solvent. The organic solvent includes ketonesolvents such as acetone, methyl ethyl ketone, cyclohexanone; estersolvents such as methyl acetate, ethyl acetate, butyl acetate, ethyllactate, methoxyethyl acetate, propylene glycol monomethyl etheracetate, ethylene glycol diacetate; ether solvents such as diethylether, ethylene glycol dimethyl ether, dioxane; aromatic solvents suchas toluene, xylene; aliphatic solvents such as pentane, hexane;halogen-containing solvents such as methylene chloride, chlorobenzene,chloroform; and alcohol solvents such as isopropyl alcohol, butanol.

Further if desired, the energy ray-curable composition may containadditives such as a pigment, a filler, a leveling agent, a defoamingagent, a thermoplastic resin, etc.

In the present invention, the protective film may be formed by applyingthe above-mentioned, energy ray-curable composition to at least onesurface of a polarizer that will be described hereinunder, according toa known coating method such as a curtain-coating method, roll-coatingmethod, flow-coating method, spray-coating method or dip-coating method,then optionally heating it at 40 to 100° C. to vaporize and remove theorganic solvent, and curing it through irradiation with energy rays, forexample, electromagnetic waves such as far-UV rays, UV rays, near-UVrays, X-rays, γ rays, or electron rays, proton rays or neutron rays.

Above all, UV rays are preferred for the energy rays in view of thefilm-forming speed (curing speed of the composition) trough irradiationwith them-, the easy availability of the energy ray-irradiation device,and the cost for the irradiation with them.

UV rays as referred to herein are those mainly falling within awavelength range of from 150 to 450 nm, and they may be generated bychemical lamps, high-pressure mercury lamps, metal halide lamps, xenonlamps, etc.

The thickness of the protective film is not specifically defined, but ispreferably at most 40 μm, more preferably at most 25 μm from theviewpoint of reducing the thickness of the film.

Not only directly formed on a polarizer, the protective film may also beformed by applying the curable composition onto a releasable sheet,followed by irradiating it with energy rays to form a film, and thethus-formed protective film may be stuck to a polarizer with a knownadhesive or paste.

The polarizer of the polarizing plate of the present invention is notspecifically defined, and may be any known one. Especially preferred forit is an iodine-colored, uniaxial-oriented film of polyvinyl alcoholresin.

Polyvinyl alcohol resin is generally produced by saponifying a polyvinylacetate prepared through polymerization of vinyl acetate. Not limited toit, however, the resin for use in the present invention may contain asmall amount of a component copolymerizable with vinyl acetate, such asthat selected from unsaturated carboxylic acids (including their salts,esters, amides, nitrites, etc.), olefins, vinyl ethers, unsaturatedsulfonic acid salts and others. The mean degree of saponification of thepolyvinyl alcohol resin is preferably from 85 to 100 mol %, morepreferably from 98 to 100 mol % for practical use of the resin. The meandegree of polymerization of the polyvinyl alcohol resin may be anydesired one.

Any known method is employable for producing the polarizer. Someconcrete methods for producing it are mentioned below. A polyvinylalcohol resin is dissolved in water or an organic solvent (e.g.,dimethylsulfoxide (DMSO), polyalcohol such as glycerin, amine such asethylenediamine) or a mixed solvent thereof with an organic solvent(having a water content of approximately from 5 to 30% by weight) toprepare a resin solution having a resin content of approximately from 5to 20% by weight, then it is formed into a film, and

(a) the film is stretched, and then colored by dipping it in an iodinesolution or a dichroic dye solution, and thereafter it is processed witha boron compound;

(b) the film is stretched and colored at the same time while it isdipped in an iodine solution or a dichroic dye solution, and then it isprocessed with a boron compound;

(c) the film is colored by dipping it in an iodine solution or adichroic dye solution, and then stretched, and thereafter it isprocessed with a boron compound; or

(d) the film is colored by dipping it in an iodine solution or adichroic dye solution, and then stretched in a boron compound solution.

Polyvinyl alcohol resin may be formed into films in any known method ofcasting, extrusion, gel film formation or the like.

It is desirable that the film of polyvinyl alcohol resin is uniaxiallystretched preferably at a temperature falling between 40 and 170° C.once or repeatedly by 3 to 10 times, preferably by 3.5 to 6 times. Inthis stage, the film may also be stretched in some degree in thedirection perpendicular to the previous uniaxial direction (in such adegree that it could prevent the shrinkage in the cross direction ormore).

The film of polyvinyl alcohol resin may be colored by contacting it withan iodine solution or with a dichroic dye-containing solution. Generallyused is an aqueous solution of iodine-potassium iodide, in which it issuitable that the iodine concentration is from 0.1 to 2 g/liter, thepotassium iodide concentration is from 10 to 50 g/liter and the ratio byweight of iodine/potassium iodide falls between 20 and 100. Practically,the time for coloration may fall between 30 and 500 seconds or so.Preferably, the temperature of the coloration bath falls between 5 and50° C. Except water, the bath may contain a small amount of an organicsolvent miscible with water. For the contact, employable is any desiredmeans of dipping, coating, spraying or the like.

The colored polyvinyl alcohol resin film is processed with a boroncompound. For example, the polyvinyl alcohol resin film is dipped in anaqueous solution of a boron compound such as boric acid or borax or inan aqueous organic solvent solution thereof (0.5 to 2 mol/liter or so),in the presence of a small amount of potassium iodide at a temperaturefalling between 50 and 70° C., or coating the film with the solution, orspraying the film with the solution. If desired, the film may bestretched while it is processed with a boron compound.

The polarizing plate of the present invention may be produced by forminga protective film on at least one surface of a polarizer, as somentioned hereinabove.

A conventional TAC film may be stuck to one or both surfaces of thepolarizing plate of the present invention with an adhesive, notdetracting from the effect of the present invention, and if desired, aknown transparent pressure-sensitive adhesive layer may be providedthereon in an ordinary method.

Especially preferably, the pressure-sensitive adhesive layer comprises,as the essential ingredient thereof, a copolymer of an acrylate such asbutyl acrylate, ethyl acrylate, methyl acrylate or 2-ethylhexylacrylate, with an α-monoolefin-carboxylic acid such as acrylic acid,maleic acid, itaconic acid, methacrylic acid or crotonic acid(optionally with a vinyl monomer such as acrylonitrile, vinyl acetate orstyrol), as not interfering with the polarizing property of thepolarizer.

In addition, transparent paste such as polyvinyl ether-type orrubber-type paste may also be used.

If desired, the polarizing plate of the present invention may belaminated with one or more functional layers such as antiglare layer,hard-coat layer, antireflection layer, half-reflection layer, reflectionlayer, luminous layer, light-diffusive layer, electroluminescent layerand others, via a adhesive or paste.

The polarizing plate of the present invention is favorably applied to atleast one surface of display panels such as liquid-crystal panels ororganic EL panels having a conventional known structure, or to at leastone surface of lenses for glasses such as sunglasses or glasses foreyesight correction.

For example, as in FIG. 1, a polarizing plate 4 formed of a polarizer 2and a protective film 3 is laminated with a λ/2 retardation film 5 and a4/λ retardation film 6 each via an adhesive layer 7 on the side oppositeto the protective film 3, and the entire laminate is stuck to onesurface of a liquid-crystal panel 1 via an adhesive layer 8; while, onthe other hand, a polarizing plate 12 is formed of a polarizer 10 coateda protective film 11 on both surfaces thereof, the polarizing plate 12is laminated with a λ/2 retardation film 13, a 4/λ retardation film 14and a viewing angle improver film 15 each via an adhesive layer 16 onone surface thereof, and the entire laminate is stuck to the othersurface of the liquid panel 1 via an adhesive layer 17. Thusconstructed, the liquid-crystal display device 9 has thin polarizingplates.

EXAMPLES

The present invention is described concretely with reference toExamples.

Examples 1a to 1d, and Comparative Examples 1a and 1b

A polyvinyl alcohol film having a degree of saponification of 99.5 mol %(75 μm thick) was well swollen by dipping it in pure water, and thencolored by dipping it in an iodine colorant solution (iodine/potassiumiodide/boric acid/pure water=0.2 g/30 g/30 g/l liter) at 35° C. for 4minutes.

The thus-colored polyvinyl alcohol film was uniaxially stretched by atleast 5 times in a stretching solution (potassium iodide/boric acid/purewater=30 g/30 g/l liter).

The thus-stretched polyvinyl alcohol film was dipped in a fixationsolution (potassium iodide/boric acid/pure water=40 g/40 g/l liter) at40° C. for 3 minutes so as to fix iodine in the film, and then the filmwas taken out of the solution and dried in a drying furnace (65° C., 5minutes) to produce a polarizer.

Next, an energy ray-curable composition that had been formulated as inTable 1 was applied to both surfaces of the thus-produced polarizer to athickness of 20 μm, and then irradiated with UV rays (wavelength, 365nm) from a metal halide lamp to an overall quantity of light of 400mJ/cm² whereby the composition was cured to form a protective film. Theprocess gave a polarizing plate.

Thus obtained, the polarizing plate was subjected to an aging test byleaving it in an environment of 60° C. and 90% RH for 100 hours. Beforeand after the aging test, the mean transmittance of the plate wasmeasured with a spectrophotometer within a wavelength range of from 400to 700 nm. When the transmittance increment before and after the agingtest is smaller than 10%, then the sample is judged good; but when it is10% or more, then the sample is judged not good. The results obtainedare shown in Table 1.

TABLE 1 Comparative Example 1 Example 1 Component a b c d a bEO-modified bisphenol A 100 60 40 20 — — diacrylate*1 Aliphaticpolyester acrylate*2 — 40 60 80 100 — 2-Ethylhexyl acrylate*3 — — — — —100 2-Hydroxy-2-methyl-1-phenylpropan- 5 5 5 5 5 5 1-one*4 Transmittancebefore aging 41.5 40.5 40.5 41.0 41.0 42.8 (%) after aging 42.9 42.542.5 43.8 85.2 80.0 rate of change (%) 3.35 4.83 4.77 6.92 108 86.7Judgment good good good good not good not good Notes: *1SR-349 bySartomer *2M-6200 by Toa Gosei *32EHA by Nippon Shokubai *4D1173(polymerization initiator) by Chiba specialty chemicals

From the results in Table 1, it is understood that, in the polarizingplates of Examples 1a to 1d that have a protective film formed of anenergy ray (UV ray)-curable composition containing at least 20% byweight of a bisphenol residue-having first energy ray-polymerizingcompound, the polyiodide was protected from discoloration though theprotective film had a thickness of 20 μm and was extremely thin, and thepolarizer was protected from external influences such as moisture, etc.

On the other hand, in the polarizing plates of Comparative Examples 1aand 1b in which the protective film was formed of a differentpolymerizing compound, polyester acrylate or 2-ethylhexyl acrylate, thepolyiodide discolored and therefore the transmittance of the platesincreased, and it is understood that the polarizing plates of thesecomparative examples are not practicable.

Examples 2a to 2d, Comparative Examples 2a and 2b

A polyvinyl alcohol film having a degree of saponification of 99.5 mol %(75 μm thick) was well swollen by dipping it in pure water, and thencolored by dipping it in an iodine colorant solution (iodine/potassiumiodide/boric acid/pure water=0.2 g/30 g/30 g/l liter) at 35° C. for 4minutes.

The thus-colored polyvinyl alcohol film was uniaxially stretched by atleast 5 times in a stretching solution (potassium iodide/boric acid/purewater=30 g/30 g/l liter).

The thus-stretched polyvinyl alcohol film was dipped in a fixationsolution (potassium iodide/boric acid/pure water=40 g/40 g/l liter) at40° C. for 3 minutes so as to fix iodine in the film, and then the filmwas taken out of the solution and dried in a drying furnace (65° C., 5minutes) to produce a polarizer.

Next, an energy ray-curable composition that had been formulated as inTable 2 was applied to both surfaces of the thus-produced polarizer to athickness of 20 μm, and then irradiated with UV rays (wavelength, 365nm) from a metal halide lamp to an overall quantity of light of 400mJ/cm² whereby the composition was cured to form a protective film. Theprocess gave a polarizing plate.

Thus obtained, the polarizing plate was subjected to an aging test byleaving it in an atmosphere at 60° C. and 90% RH for 100 hours. Beforeand after the aging test, the mean transmittance of the plate wasmeasured with a spectrophotometer within a wavelength range of from 400to 700 nm. When the transmittance increment before and after the agingtest is smaller than 10%, then the sample is judged good; but when it is10% or more, then the sample is judged not good. The results obtainedare shown in Table 2.

TABLE 2 Comparative Example 2 Example 2 a b c d a b CompositionNeopentyl glycol 100 80 60 40 20 0 hydroxypivalate diacrylate Polyesteracrylate 0 20 40 60 80 100 Polymerization 5 5 5 5 5 5 initiator Silanecoupling 6 6 6 6 6 6 agent Transmittance before aging 39.40 41.00 40.3040.70 40.50 40.20 (%) after aging 41.10 42.30 41.90 42.60 46.30 89.30rate of change (%) 4.29 3.12 1.05 4.67 14.40 121.97 Judgment good goodgood good not good not good

In Table 2, neopentyl glycol hydroxypivalate diacrylate is “MANDA”, atrade name by Nippon Kayaku, and this is a type of the second energyray-polymerizing compound. The polyester acrylate is “M-6200” a tradename by Toa Gosei, and this is a type of the fifth energyray-polymerizing compound. The initiator is “D1173”, a trade name byChiba specialty chemicals; and the silane coupling agent isγ-acryloxypropyltriethoxysilane (“KBM-5103, a trade name by Shin-etsuSilicone).

From the results in Table 2, it is understood that, in the polarizingplates of Examples 2a to 2d in which the amount of the second energyray-polymerizing compound was at least 40% by weight of the resin solidcontent of the composition (total of neopentyl glycol hydroxypivalatediacrylate and polyester acrylate), the polyiodide was protected fromdiscoloration though the protective film had a thickness of 20 μm andwas extremely thin, and the polarizer was protected from externalinfluences such as moisture, etc.

On the other hand, in the polarizing plates of Comparative Examples 2aand 2b in which the amount of the second energy ray-polymerizingcompound was smaller than 40% by weight of the resin solid content ofthe composition, the polyiodide discolored and therefore thetransmittance of the plates increased after the aging test, and it isunderstood that the polarizing plates of these comparative examples arenot practicable.

Examples 3a to 3c, Comparative Examples 3a to 3c

Polarizing plates of Examples 3a to 3c and Comparative Examples 3a to 3cwere produced under the same condition as in Examples 2a to 2d, forwhich, however, energy ray-curable compositions as in Table 3 below wereused in place of the energy ray-curable compositions for Examples 2a to2d mentioned above. Also under the same condition as in Examples 2a to2d, the transmittance of the plates was measured. The data and theevaluation results are shown in Table 3 below.

TABLE 3 Example 3 Comparative Example 3 a b c a b c CompositionEO-modified TMPTA 100 80 60 40 20 0 Polyester acrylate 0 20 40 60 80 100Polymerization 5 5 5 5 5 5 initiator Silane coupling agent 6 6 6 6 6 6Transmittance before aging 41.40 40.70 39.70 39.60 41.40 40.20 (%) afteraging 42.80 42.80 42.50 53.50 67.50 89.30 rate of change (%) 3.50 5.217.10 35.10 63.13 121.97 Judgment good good good not good not good notgood

In Table 3, EO-modified TMPTA (trimethylolpropane triacrylate) is“SR-454”, a trade name by Sartomer, and this is a type of the thirdenergy ray-polymerizing compound. The polyester acrylate, thepolymerization initiator and the silane coupling agent are the same asthose used in Examples 2a to 2d.

As is obvious from Table 3 above, it is understood that the rate oftransmittance change of the polarizing plates of Examples 3a to 3c inwhich the amount of the third energy ray-polymerizing compound was atleast 60% by weight of the resin solid content of the composition (totalof EO-modified TMPTA and polyester acrylate) was smaller than that ofthe polarizing plates of Comparative Examples 3a to 3c, and though theprotective film in the polarizing plates of these Examples 3a to 3c hada thickness of 20 μm and was extremely thin, the polyiodide in theplates was protected from discoloration and the polarizer of the plateswas protected from external influences such as moisture, etc.

On the other hand, in the polarizing plates of Comparative Examples 3ato 3c in which the amount of the third energy ray-polymerizing compoundwas at most 40% by weight of the resin solid content of the composition,the polyiodide discolored and therefore the transmittance of the platesincreased after the aging test, and it is understood that the polarizingplates of these comparative examples are not practicable.

Example 4a, Comparative Examples 4a to 4e

Polarizing plates of Example 4a and Comparative Examples 4a to 4e wereproduced under the same condition as in Examples 2a to 2d, for which,however, energy ray-curable compositions as in Table 4 below were usedin place of the energy ray-curable compositions for Examples 2a to 2dmentioned above. Also under the same condition as in Examples 2a to 2d,the transmittance of the plates was measured. The data and theevaluation results are shown in Table 4 below.

TABLE 4 Example Comparative Example 4a 4a 4b 4c 4d 4e CompositionDipentaerythritol 100 80 60 40 20 0 triacrylate Polyester 0 20 40 60 80100 acrylate Polymerization 5 5 5 5 5 5 initiator Silane coupling 6 6 66 6 6 agent Transmittance before aging 40.80 40.50 40.70 41.10 40.3040.20 (%) after aging 44.00 49.30 58.00 73.00 81.00 89.30 rate of change7.92 21.87 42.42 77.67 101.04 121.97 (%) Judgment good not good not goodnot good not good not good

In Table 4, dipentaerythritol triacrylate is “SR-454”, a trade name bySartomer, and this is a type of the fourth energy ray-polymerizingcompound. The polyester acrylate, the polymerization initiator and thesilane coupling agent are the same as those used in Examples 2a to 2d.

As is obvious from Table 4 above, it is understood that the rate oftransmittance change of the polarizing plate of Example 4a in which theresin solid matter in the composition was the fourth energyray-polymerizing compound alone was smaller than that of the polarizingplates of Comparative Examples 4a to 4e, and though the protective filmin the polarizing plate of the Example had a thickness of 20 μm and wasextremely thin, the polarizer of the plate was protected from externalinfluences such as moisture, etc.

On the other hand, the rate of transmittance change of the polarizingplates of Comparative Examples 4a to 4e in which the amount of polyesteracrylate, which is the fifth energy ray-polymerizing compound in thecomposition was 20% by weight or more of the resin solid content of thecomposition was extremely large as compared with that of the polarizingplate of Example 4a, and it is understood that the polarizing plates ofthese comparative examples are not practicable.

Example 5

A polarizing plate of Example 5 was produced under the same condition asin Examples 2a to 2d, for which, however, an energy ray-curablecomposition as in Table 5 below was used in place of the energyray-curable compositions for Examples 2a to 2d mentioned above. Alsounder the same condition as in Examples 2a to 2d, the transmittance ofthe plate was measured. The data and the evaluation result are shown inTable 5 below.

TABLE 5 Example 5 Composition EO-modified Bis-A acrylate 50 Neopentylglycol hydroxypivalate diacrylate 50 Polymerization initiator 5 Silanecoupling agent 6 Transmittance before aging 42.70 (%) after aging 43.90rate of change (%) 2.98 Judgment good

In Table 5, EO-modified Bis-A acrylate is “SR-349”, a trade name bySartomer, and this is a type of the first energy ray-polymerizingcompound that has a bisphenol A-type group.

Neopentyl glycol hydroxypivalate diacrylate is “MANDA”, a trade name byNippon Kayaku, and this is a type of the second energy ray-polymerizingcompound. The polymerization initiator and the silane coupling agent arethe same as those used in Examples 2a to 2d.

As is obvious from Table 5 above, it is understood that the rate oftransmittance change of the polarizing plate of Example 5 that containsboth the first energy ray-polymerizing compound and the second energyray-polymerizing compound was small enough for practical use, and thoughthe protective film in the polarizing plate had a thickness of 20 μm andwas extremely thin, the polarizer of the plate was protected fromexternal influences such as moisture, etc.

Example 6

A polarizing plate of Example 6 was produced under the same condition asin Examples 2a to 2d, for which, however, an energy ray-curablecomposition as in Table 6 below was used in place of the energyray-curable compositions for Examples 2a to 2d mentioned above. Alsounder the same condition as in Examples 2a to 2d, the transmittance ofthe plate was measured. The data and the evaluation result are shown inTable 6 below.

TABLE 6 Example 6 Composition EO-modified Bis-F diacrylate 50 Neopentylglycol hydroxypivalate diacrylate 50 Polymerization initiator 5 Silanecoupling agent 6 Transmittance before aging 42.45 (%) after aging 43.62rate of change (%) 2.76 Judgment good

In Table 6, EO-modified Bis-F diacrylate is “R-712”, a trade name byNippon Kayaku, and this is a type of the first energy ray-polymerizingcompound that has a bisphenol F-type group.

Neopentyl glycol hydroxypivalate diacrylate is “MANDA”, a trade name byNippon Kayaku, and this is a type of the second energy ray-polymerizingcompound. The polymerization initiator and the silane coupling agent arethe same as those used in Examples 2a to 2d.

As is obvious from Table 6 above, it is understood that the rate oftransmittance change of the polarizing plate of Example 6 that containsboth the bisphenol F-type group-having, first energy ray-polymerizingcompound and the second energy ray-polymerizing compound was smallenough for practical use, and though the protective film in thepolarizing plate had a thickness of 20 μm and was extremely thin, thepolarizer of the plate was protected from external influences such asmoisture, etc.

INDUSTRIAL APPLICABILITY

In the polarizing plate of the present invention, though the protectivefilm is thin, the polarizer is protected from the influence of externalmoisture and the like, and therefore its polarizability is kept goodeven in high-temperature high-humidity environments.

1. A polarizing plate having a polarizer obtained from iodine-coloring apolyvinyl alcohol resin film, and a protective film directly formed onboth surfaces of the polarizer, wherein the protective film has athickness of 40 μm or less, and is formed by applying an energyray-curable composition to the polarizer and irradiating the appliedenergy ray-curable composition with ultraviolet rays to polymerize andcure the energy ray-curable composition, wherein the energy ray-curablecomposition comprises an energy ray-polymerizing compound having aneopentylglycol group in an amount of at least 40% by weight in terms ofa resin solid content thereof, selected from the group consisting of:

the polyvinyl alcohol is dyed only with iodine.
 2. The polarizing plateaccording to claim 1, wherein the energy ray-curable compositioncontains the first energy ray-polymerizing compound having a bisphenolresidue.
 3. The polarizing plate according to claim 2, wherein theenergy ray-curable composition comprises the energy ray-polymerizingcompounds in an amount of 50% by weight in terms of the resin solidcontent thereof.
 4. The polarizing plate according to claim 2, whereinthe energy ray-polymerizing compound having a bisphenol residue has abisphenol A-type group.
 5. The polarizing plate according to claim 2,wherein the energy ray-polymerizing compound having a bisphenol grouphas a bisphenol F-type group.
 6. The polarizing plate according to claim1, wherein the energy ray-curable composition further comprises anenergy ray-polymerizing compound that comprises a polyester(meth)acrylate.
 7. A liquid-crystal display device having a liquidcrystal panel, and the polarizing plate of any of claim 1 provided on atleast one surface of the liquid-crystal panel.
 8. A polarizing platehaving a polarizer obtained form iodine-coloring a polyvinyl alcoholresin film, and a protective film directly formed on both surfaces ofthe polarizer, wherein the protective film has a thickness of 40 μm orless, and is formed by applying and energy ray-curable composition tothe polarizer and irradiating the applied energy ray-curable compositionwith ultraviolet rays to polymerize and cure the energy ray-curablecomposition, wherein, the energy ray-curable composition that comprisesat least one of (a) an energy ray-polymerizing compound having aneopentylglycol group, and (b) an energy ray-polymerizing compoundhaving a pentaerythritol group, the energy ray polymerizing compoundhaving a neopentylglycol group is selected from the group consisting of:

the energy ray polymerizing compound having a pentaerithritol group isone of the following chemical formulae:

in which R represents a hydrogen atom or a methyl group, the polyvinylalcohol is dyed only with iodine, and the energy ray-curable compositioncomprises an energy ray-polymerizing compound having atrimethylolpropane group in an amount of a least 60% by weight in termsof the resin solid content thereof.
 9. The polarizing plate according toclaim 8, wherein the energy ray-curable composition further comprisesand energy ray-polymerizing compound having a bisphenol residue.
 10. Thepolarizing plate according to claim 9, wherein the energy ray-curablecomposition comprises the energy ray-polymerizing compound having abisphenol residue in an amount of at least 20% by weight in terms of theresin solid content thereof.
 11. The polarizing plate according to claim9, wherein the energy ray-polymerizing compound having a bisphenolresidue has a bisphenol A-type group.
 12. The polarizing plate accordingto claim 9, wherein the energy ray-polymerizing compound having abisphenol group has a bisphenol F-type group.
 13. The polarizing plateaccording to claim 8, wherein the energy ray-curable composition furthercomprises and energy ray-polymerizing compound that comprises apolyester (meth) acrylate.
 14. A liquid-crystal display device having aliquid crystal panel, and the polarizing plate of claim 8, provided onat least one surface of the liquid-crystal panel.
 15. A polarizing platehaving a polarizer obtained from iodine-coloring a polyvinyl alcoholresin film, and a protective film directly formed on both surfaces ofthe polarizer, wherein the protective film has a thickness of 40 μm orless, and is formed by applying an energy ray-curable composition to thepolarizer and irradiating the applied energy ray-curable compositionwith ultraviolet rays to polymerize and cure the energy ray-curablecomposition, wherein the energy ray-curable composition consists of anyenergy ray-polymerizing compound having a pentaerythritol group selectedfrom the group consisting of:

in which R represents a hydrogen atom or a methyl group, and thepolyvinyl alcohol is dyed only with iodine.